This invention relates to a flexible coupling for connecting lengths of tubing. It relates more particularly to a coupling of this type which maintains a fluid-tight seal between the tubing lengths yet permits a certain degree of relative motion between those lengths.
The tubing with which we are concerned here is often used to convey fluids at relatively high pressure and/or at relatively high or low temperatures. Also the tubing is employed in applications in which the tubing is stressed, i.e. in an airplane wing for example. Accordingly, when connecting together lengths of tubing it is imperative that a coupling be employed which is able to permit relative sliding motion between the tubing lengths to prevent stress from developing or increasing, while at the same time providing an effective fluid-tight seal at the joint.
There exist various types of tubing couplings which are intended to accomplish that. Some such couplings are disclosed in U.S. Pat. Nos. 3,186,739, 3,753,205 and 3,891,291. However, they all suffer one or more drawbacks which tend to limit their use and application. Some do not flex sufficiently. Some have an excessive number of critical parts leading to reliability and tolerance accumulation problems. In other words, failure of a single, critical, small component in the coupling can cause total failure of the coupling. Bearing in mind that a coupled tubing may carry a toxic fluid or a fluid under high pressure or at high temperature, it is apparent that failure of the coupling can cause property damage and injury to persons in the vicinity of a tubing.
Also when some existing couplings are pressure-loaded with an angular misalignment of the joined-together tubing, the load is concentrated at a particular point or points within the coupling. This causes excessively high stresses on certain components of the coupling which tend to deform those components. Such deformities can cause fluid leakage past the seals between the coupling and the tubing. This is particularly so in the case of couplings employing resilient dynamic O-ring seals to maintain the fluid-tight integrity of the coupling. That problem is exacerbated for that type prior coupling if the seal has dried out with age or is maintained at a relatively high or low temperature for any appreciable length of time. Indeed such couplings cannot operate at all at temperatures too high for elastomeric seals.